Midrasch zu Bereschit 29:13

When Laban heard the tidings of Jacob, the son of his sister, and the power of his might which he had displayed at the well, he ran to meet him, to kiss him, and to embrace him, as it is said, "And it came to pass, when Laban heard the tidings of Jacob, his sister's son" (Gen. 29:13). "And Laban said unto Jacob, Because thou art my brother" (Gen. 29:15). Was he then his brother? Was he not the son of his sister? This teaches thee that the son of a man's sister is like his son, and the son of a man's brother || is like his brother. Whence do we learn (this)? From Abraham, our father, because it is said, "And Abram said to Lot, Let there not be strife… for we are brethren" (Gen. 13:8). Another verse (says), "And when Abram heard that his brother was taken captive" (Gen. 14:14). Was he his brother? Was he not the son of his brother? But it teaches thee that the sons of a man's brother are like his own brothers.